DE102016008842A1 - Method and device for preparing comminuted plastic parts for electrostatic separation - Google Patents

Abstract

The invention relates to a method and a device for treating comminuted plastic parts prior to electrostatic separation of the plastic parts into individual plastic fractions. In the method, at least a part of the surface of the plastic parts, which prevents electrostatic charging, mechanically roughened or mechanically destroyed. Thereafter, the treated parts are electrostatically neutralized. For the mechanical treatment, a tool is provided, the z. B. mechanically roughened with several cutting the surface of the plastic parts and at least partially destroyed the surface.

Description

Mixed plastics, as they occur, for example, in the processing of PET bottles, electronic scrap and the like, are usually separated by a combination of wet and dry treatment processes and then separated into fractions that are as pure as possible.

For plastic separation, swimming-sink procedures are often used, in which the plastics can be separated on the basis of their density or their specific weight. In the subsequent separation into individual types of plastics, various methods are used, such as sorting in the near infrared or electrostatic separation technology.

When plastics are processed, for example, from electronic waste, toner cartridges or the like, the vast majority of black-colored plastic parts. For the separation of such plastics are essentially only electrostatic process into consideration.

Electrostatic separation processes exploit triboelectric effects for separation. The shredded plastic parts are mutually charged by intensive contact with each other. One plastic is charged positively, the other negative. The subsequent electrostatic separation in a high voltage field using positively and negatively poled electrodes is then no problem. The purity of the separated products is optimized via butterfly valves.

Electrostatic effects are pure surface effects, i. h., it is charged exclusively the surface of the plastic parts.

The problem now is when the plastic parts are influenced in particular by chemical effects on the surface. This is z. B. possible if the plastic parts are chemically altered by strong alkalis, salt solutions or the like, as they occur in part in the sink-float separation on its surface. In this case, for example, certain chemical compounds or individual atoms can be incorporated into the surface of the plastics. This then leads to the subsequent electrostatic separation to the fact that the plastic particles can no longer or only slightly charged. This process is also not reversible by washing with water or other chemicals.

The invention has for its object, plastic parts, and in particular those plastic parts with "passive" surfaces that can not or only insufficiently electrostatically charged to prepare for electrostatic separation.

This object is achieved according to the invention for a method according to the invention by the features of patent claim 1.

The features of a device according to the invention are contained in the independent claim.

Accordingly, prior to the electrostatic separation of the plastic particles whose surface is roughened intensively, wherein preferably at least a portion whose surface is mechanically destroyed and removed.

It is presented with the present invention, a mechanical method to the z. B. by chemical pretreatment "passive" surface of the plastic parts to destroy and roughen partially. So you deliberately hurt the surface to get back "active" and electrostatically chargeable plastic parts.

It should be noted that known methods of surface treatment, such as hammer mills or similar methods, are not effective because the chemically contaminated surfaces of the plastic particles to be charged are essentially only reshaped, but not destroyed or removed.

Of course, the method can also be used if the surface of the plastic parts is not covered by a "passive" layer. In any case, for example with soiled plastic parts, areas are exposed that can be electrostatically charged.

For carrying out the invention z. B. the plastic parts are brushed with hard steel bristles, so that a part of the surface removed and thus reactivated. Other methods are possible, such. As rotating mills in which the plastic parts are exposed to a variety of abrasive particles, so that their surface is at least partially destroyed again and can be charged by it.

Further embodiments of the invention will become apparent from the dependent claims.

The invention is explained in more detail with reference to the drawing. In this represent:

1 : Schematically the pretreatment of plastic particles before electrostatic separation;

2 : Schematically a representation of the electrostatic charge of plastic particles;

3 : A schematic representation of the treatment of the surface of plastic particles by means of mechanical brushes;

4 : A schematic representation of an apparatus for treating the surface of plastic particles;

5 : A partial representation of the support for receiving the plastic particles to be treated;

6 : Another illustration of the support for the plastic particles;

7 : Schematically a representation of a machine for brushing the surface of plastic particles;

8th : Part of a longitudinal section through a machine according to 7 for brushing the surface of plastic particles;

9 : Schematically another embodiment of a machine for treating the surface of plastic particles; and

10 : a flowchart of the methods according to the invention.

According to 1 become plastic particles 1 placed in a separation vessel X, the z. B. is filled with a liquid M to prepare a swim-sink separation process. Depending on the type of liquid M will be the surface of the treated article 1' through a thin layer 2 coated. Depending on the liquid used M, this layer 2 cause the article 1' is "passivated" so to speak and can not be electrostatically charged or only slightly charged.

Usually, the plastic particles are charged triboelectrically by intensive contact of the particles with each other for the electrostatic separation. As 2 shows, the plastic particle A is brought by a force F in intensive contact with a particle B, which also acts with a force F 'on the other particle. At the moment of particle contact, electrons emerge from one plastic and are absorbed by the other plastic. The plastic, where the electrons are released, is charged positively, the plastic, which absorbs the electrons, is negatively charged.

If, as in 2 shown, the surface of the plastic particles by a pretreatment is "passivated", ie that the plastic A 'through a passive layer 2 and the plastic B 'also through a passive layer 2 ' is coated on the surface, there is no or only a slight electrostatic charge, so that an electrostatic separation is not possible.

As tests have shown, it is not possible to reactivate this passive layer on the surface, for example by washing or additional chemical treatment.

For the activation of the surface z. B. by a flame, as used for example in the painting of polypropylene (PP) bumpers as a pretreatment, must be dispensed with small plastic particles due to the risk of fire. An activation of the surface of the plastic particles by corona or plasma treatments would also be possible, but is sometimes too expensive for practical use and does not always give the desired results.

According to the invention, the activation of the surface of the plastic particles takes place by removing the "passive" layer in particular by at least partially mechanical destruction thereof.

As in 3 shown, the particle A by a mechanical device, preferably a brush 8th processed. The hard bristles, ideally steel bristles 8th respectively. 8th' are guided relative to the particle surface in the direction X on the surface over. In this case, there is a targeted violation of the surface of the plastic particles and a total or partial removal of the passive layer 2 , When removing the passive layer 2 can then remove the removed particles 6 the passive layer can be removed in the form of a dust.

The now free "bare" surface areas 5 , which are no longer covered with a passive layer, can now electrostatically activated and charged again. This is also possible if parts of the surface 4 are still passivated. So there is no complete surface cleaning to recharge the plastic particles electrostatically.

In 4 schematically an embodiment of a brushing machine is shown, with which the surface of plastic particles for electrostatic charging can be treated. The brushing machine has bristles 8th which ideally consist of hard steel wires and in a bristle carrier 9 are attached. This brush arrangement is guided in the direction X over the surface of the plastic particles A. These lie on the surface of an overlay or counter bearing 10 on. This counter bearing 10 may be, for example, a wire screen, a corrugated or textured surface or assume another shape. Ideally, this mating surface has sharp edges 11 , which can also lead to the injury of the surface of the plastic particles. Between individual counter bearings 10 respectively. 10 ' is ideally a gap 13 arranged in the dust particles 12 . 12 ' - which can occur during mechanical damage to the surfaces of the plastic particles - can escape.

In order to ensure optimum damage to the surfaces of the plastic particles, it is advisable to use as bristles the shortest possible high-hardness steel wires. Too long or too thin steel wires, which are still too soft, there is no sufficient violation of the surfaces. The separation results are then much worse than with hard wire bristles.

An abutment or support for plastic particles to be treated is in 5 shown.

The counter bearing is a polygonal, z. B. Square steel wire woven wire. In contrast to a sieve with round wires, in which no violation of the surface of the plastic particles takes place, this is possible with a sieve with square or rectangular cross-section of the wire. The sharp edges of warp or weft threads 15 respectively. 16 of the screen also cause the plastic particles are injured on their surface. The thereby removed dust particles 12 can then be easily discharged through the screen gaps.

In 6 is shown another embodiment of the abutment or support for the plastic particles. Here, a surface produced from sharp-edged metal structures is used. These metal structures, which ideally have a sloping surface, will have a sharp edge 22 the violation of the surface of the plastic particles achieved when the plastic particles are moved with a certain pressure on the anvil in any direction.

The sharp-edged metal structures are z. B. Rectangular rods 20 , The eroded plastic dust can over gaps 21 between the parts 20 be discharged.

It is also possible, the support or counter bearing for the plastic particles as a closed, provided with a mechanical structure metal part 26 train. edge 25 and sloping surfaces 24 The structure also lead here to the mechanical violation of the surface of the plastic particles to be treated. The dust generated is then separated from the plastic mixture by dedusting or air classification.

In 7 a brushing machine is shown schematically. In a housing 30 there is a strainer basket 38 , which is equipped with the mentioned rectangular wires in the form of a mesh fabric. Inside the screen room, an axle rotates 31 on which several arms 32 are attached. These arms carry at their outer end 33 the brush holders described above 34 with wire brushes 35 ,

The counter bearing or support for the plastic particles forming structure 36 is as a cylindrical strainer basket 38 executed.

By rotation of the axis 31 with the associated brushes, the plastic particles are brushed continuously, whereby always a part of their surface is mechanically destroyed. By using a plurality of brush sets, which may be staggered, a depassivation or activation of the plastic particles can be carried out over a longer strainer section. The removed from the surface of the plastic particles plastic dust 39 gets down from the case 30 discharged. The plastic particles can also during the brushing process in the direction of the axis 31 be transported. Thus, a continuous process is possible in which plastic parts are continuously fed and discharged.

In 8th a schematic longitudinal section through a brushing machine according to the invention is shown. The plastic particles to be treated 45 Beyond an opening and a funnel 44 into the interior of a machine housing 30 given. By a snail 43 the material is now in the area of a screen basket 38 promoted. Inside the strainer basket rotates by a motor 41 , driven with adjustable speed, the brush system. Various brush sets are arranged one behind the other to perform maximum surface activation of the treated plastic particles. The brushed material falls through a discharge opening 46 out of the machine while the fines or the brushed dust 47 through a funnel 42 is discharged down.

In the embodiment of a brushing machine according to 9 are brushes 53 on the underside of a rotating disc 50 arranged. This disc rotates with the adjustable speed brushes located at the bottom of the disc 52 , In the middle of the disc, the plastic particles are in a filling opening 51 entered. Below the disc 50 there is a fixed disc 55 with a corrugated or otherwise structured surface serving for separation. This disc is fixed. The brushes now rotate at a certain speed and a certain distance above the fixed or counter-rotating disc.

The plastic particles between the two mutually rotating discs are activated by the brush system and then discharged out of the system to the outside.

Alternatively, it is also possible the upper disc 50 fixed and the lower disc to rotate or to let the discs rotate in opposite directions.

In 10 symbolically illustrates the entire process of activating plastic particles using mechanical brushes.

material 60 gets into a brushing machine or a brushing machine 61 given. Removed material of the individual plastic particles is discharged from this brushing apparatus and, for example, in a device 62 sucked off and then in a station 63 packaged.

From the brushing machine discharged material 64 is via a neutralization unit 65 electrostatically neutralized. This is done using a high voltage neutralizer powered by AC voltage. By an alternating voltage with, for example, +/- 7000 volts, the charged plastic particles are neutralized. These are after neutralization in a reservoir 66 given.

As it has been shown, it may make sense to let these particles rest for a certain time T, so that any remaining surface charges can further degrade. Under certain circumstances, these surface charges are rectified, so that different plastics have the same surface charge due to the brushing process. This is negative for a subsequent electrostatic separation, because one of the plastics has to be reloaded by the electrostatic charging process.

With a method according to the invention it is also advantageous to be able to mechanically abrade the impurities adhering to the surface of the plastic particles by a mechanical "destruction" of the surface of plastic particles. This increases the quality of the obtained plastic fraction.

Claims (10)

A method for treating crushed plastic parts prior to electrostatic separation of the plastic parts into individual plastic fractions, characterized in that at least a part of the surface of the plastic parts is mechanically roughened or mechanically destroyed. A method according to claim 1, characterized in that the part of the surface of the plastic parts, which prevents electrostatic charging of the plastic parts or insufficiently possible, at least partially mechanically removed or destroyed. Method according to one of the preceding claims, characterized in that the plastic parts are electrostatically neutralized after the mechanical treatment. Apparatus for treating shredded plastic parts according to the method according to claim 1, characterized in that the device comprises a tool which mechanically roughen the surface of the plastic parts and at least partially destroys the surface. Apparatus according to claim 4, characterized in that the tool has at least one carrier for a plurality of sharp-edged cutting, which is moved over the plastic parts. Apparatus according to claim 5, characterized in that the carrier receives hard metal bristles. Device according to one of claims 4 to 6, characterized in that for receiving the plastic parts, an abutment is provided which has a plurality of sharp-edged cutting. Apparatus according to claim 7, characterized in that the counter bearing is a sieve of sharp-edged wires. Device according to one of claims 4 to 8, characterized in that carrier and counter bearing move in opposite directions to each other. Apparatus according to claim 9, characterized in that carrier and abutment are arranged on two opposite, counter-rotating, rotating about a common axis discs.

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